2015-08-02T18:32:12ZModulation of electrical stimulation applied to human physiology and clinical diagnostichttp://hdl.handle.net/10362/15243
Título: Modulation of electrical stimulation applied to human physiology and clinical diagnostic
Autor: Araújo, Tiago Sérgio Santos Rodrigues
Resumo: The use, manipulation and application of electrical currents, as a controlled interference mechanism in the human body system, is currently a strong source of motivation to researchers in areas such as clinical, sports, neuroscience, amongst others. In electrical stimulation (ES), the current applied to tissue is traditionally controlled concerning stimulation
amplitude, frequency and pulse-width. The main drawbacks of the transcutaneous
ES are the rapid fatigue induction and the high discomfort induced by the non-selective
activation of nervous fibers.
There are, however, electrophysiological parameters whose response, like the response
to different stimulation waveforms, polarity or a personalized charge control, is still
unknown. The study of the following questions is of great importance:
What is the physiological effect of the electric pulse parametrization concerning
charge, waveform and polarity? Does the effect change with the clinical condition of
the subjects?
The parametrization influence on muscle recruitment can retard fatigue onset?
Can parametrization enable fiber selectivity, optimizing the motor fibers recruitment
rather than the nervous fibers, reducing contraction discomfort?
Current hardware solutions lack flexibility at the level of stimulation control and
physiological response assessment. To answer these questions, a miniaturized, portable
and wireless controlled device with ES functions and full integration with a generic
biosignals acquisition platform has been created. Hardware was also developed to provide complete freedom for controlling the applied current with respect to the waveform,
polarity, frequency, amplitude, pulse-width and duration.
The impact of the methodologies developed is successfully applied and evaluated in
the contexts of fundamental electrophysiology, psycho-motor rehabilitation and neuromuscular disorders diagnosis.
This PhD project was carried out in the Physics Department of Faculty of Sciences and
Technology (FCT-UNL), in straight collaboration with PLUX - Wireless Biosignals S.A. company and co-funded by the Foundation for Science and Technology.2015-06-01T00:00:00ZDesign, implementation, and performance of a distributed and scalable sensor system for critical distance measurements in the CMS detector at LHChttp://hdl.handle.net/10362/14784
Título: Design, implementation, and performance of a distributed and scalable sensor system for critical distance measurements in the CMS detector at LHC
Autor: Antunes, João Filipe Rodrigues
Resumo: The “CMS Safety Closing Sensors System” (SCSS, or CSS for brevity) is a remote
monitoring system design to control safety clearance and tight mechanical movements
of parts of the CMS detector, especially during CMS assembly phases. We present the
different systems that makes SCSS: its sensor technologies, the readout system, the data
acquisition and control software. We also report on calibration and installation details,
which determine the resolution and limits of the system.
We present as well our experience from the operation of the system and the analysis of the
data collected since 2008. Special emphasis is given to study positioning reproducibility
during detector assembly and understanding how the magnetic fields influence the
detector structure.2014-12-01T00:00:00ZCharacterization of molecular damage induced by UV photons and carbon ions on biomimetic heterostructureshttp://hdl.handle.net/10362/14634
Título: Characterization of molecular damage induced by UV photons and carbon ions on biomimetic heterostructures
Autor: Gomes, Paulo Jorge Pereira
Resumo: The study of the effect of radiation on living tissues is a rather complex task to address mainly because they are made of a set of complex functional biological structures and interfaces. Particularly if one is looking for where damage is taking place in a first stage and what are the underlying reaction mechanisms. In this work a new approach is addressed to study the effect of radiation by making use of well identified molecular hetero-structures samples which mimic the biological environment. These were obtained by assembling onto a solid support deoxyribonucleic acid (DNA) and phospholipids together with a soft water-containing polyelectrolyte precursor in layered structures and by producing lipid layers at liquid/air interface with DNA as subphase. The effects of both ultraviolet (UV) radiation and carbon ions beams were systematically investigated in these heterostructures, namely damage on DNA by means vacuum ultraviolet (VUV), infrared (IR), X-Ray Photoelectron (XPS) and impedance spectroscopy. Experimental results revealed that UV affects furanose, PO2-, thymines, cytosines and adenines groups. The XPS spectrometry carried out on the samples allowed validate the VUV and IR results and to conclude that ionized phosphate groups, surrounded by the sodium counterions, congregate hydration water molecules which play a role of UV protection. The ac electrical conductivity measurements revealed that the DNA electrical conduction is arising from DNA chain electron hopping between base-pairs and phosphate groups, with the hopping distance equal to the distance between DNA base-pairs and is strongly dependent on UV radiation exposure, due loss of phosphate groups. Characterization of DNA samples exposed to a 4 keV C3+ ions beam revealed also carbon-oxygen bonds break, phosphate groups damage and formation of new species. Results from radiation induced damage carried out on biomimetic heterostructures having different compositions revealed that damage is dependent on sample composition, with respect to functional targeted groups and extent of damage. Conversely, LbL films of 1,2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (Sodium Salt) (DPPG) liposomes, alternated with poly(allylamine hydrochloride) (PAH) revealed to be unaffected, even by prolonged UV irradiation exposure, in the absence of water molecules. However, DPPG molecules were damaged by the UV radiation in presence of water with cleavage of C-O, C=O and –PO2- bonds. Finally, the study of DNA interaction with the ionic lipids at liquid/air interfaces revealed that electrical charge of the lipid influences the interaction of phospholipid with DNA. In the presence of DNA in the subphase, the effects from UV irrladiation were seen to be smaller, which means that ionic products from biomolecules degradation stabilize the intact DPPG molecules. This mechanism may explain why UV irradiation does not cause immediate cell collapse, thus providing time for the cellular machinery to repair elements damaged by UV.2014-12-01T00:00:00Z40 K neon liquid energy storage unithttp://hdl.handle.net/10362/14630
Título: 40 K neon liquid energy storage unit
Autor: Martins, Daniel Filipe
Resumo: Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical
vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensor’s sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to
turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocooler’s temperature that increases when turned OFF.
In this work, several prototypes working around 40 K were designed, built and characterized.
They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect
in a porous material.
Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions.
A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature
((≈ 40K ±1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler.
This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices,implemented as a software, describes quite well the experimental results. Solutions to improve these devices are also proposed.2014-12-01T00:00:00Z